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Electrode

An electrode is an electrical conductor that is used to make contact with a metallic part of a circuit. The anode is the electrode where oxidation takes place. The cathode is the electrode where reduction takes place.

The zinc sulphate and copper sulphate solutions are called the electrolyte solutions.

Electrolyte

An electrolyte is a substance that contains free ions and which therefore behaves as an electrical conductor.

The U-tube also plays a very important role in the cell. In the Zn/Zn 2 + half-cell, there is a build up of positive charge because of the release of electrons through oxidation. In the Cu 2 + /Cu half-cell, there is a decrease in the positive charge because electrons are gained through reduction. This causes a movement of SO 4 2 - ions into the beaker where there are too many positive ions, in order to neutralise the solution. Without this, the flow of electrons in the outer circuit stops completely. The U-tube is called the salt bridge . The salt bridge acts as a transfer medium that allows ions to flow through without allowing the different solutions to mix and react.

Salt bridge

A salt bridge, in electrochemistry, is a laboratory device that is used to connect the oxidation and reduction half-cells of a galvanic cell.

The galvanic cell

In the zinc-copper cell the important thing to notice is that the chemical reactions that take place at the two electrodes cause an electric current to flow through the outer circuit. In this type of cell, chemical energy is converted to electrical energy . These are called galvanic cells . The zinc-copper cell is one example of a galvanic cell. A galvanic cell (which is also sometimes referred to as a voltaic or electrochemical cell) consists of two metals that are connected by a salt bridge between the individual half-cells. A galvanic cell generates electricity using the reactions that take place at these two metals, each of which has a different reaction potential .

So what is meant by the 'reaction potential' of a substance? Every metal has a different half reaction and different dissolving rates. When two metals with different reaction potentials are used in a galvanic cell, a potential difference is set up between the two electrodes, and the result is a flow of current through the wire that connects the electrodes. In the zinc-copper cell, zinc has a higher reaction potential than copper and therefore dissolves more readily into solution. The metal 'dissolves' when it loses electrons to form positive metal ions. These electrons are then transferred through the connecting wire in the outer circuit.

Galvanic cell

A galvanic (voltaic) cell is an electrochemical cell that uses a chemical reaction between two dissimilar electrodes dipped in an electrolyte, to generate an electric current.

Interesting fact

It was the Italian physician and anatomist Luigi Galvani who marked the birth of electrochemistry by making a link between chemical reactions and electricity. In 1780, Galvani discovered that when two different metals (copper and zinc for example) were connected together and then both touched to different parts of a nerve of a frog leg at the same time, they made the leg contract. He called this "animal electricity". While many scientists accepted his ideas, another scientist, Alessandro Volta, did not. In 1800, because of his professional disagreement over the galvanic response that had been suggested by Luigi Galvani, Volta developed the voltaic pile , which was very similar to the galvanic cell. It was the work of these two men that paved the way for all electrical batteries.

For the following cell:

Z n | Z n 2 + | | A g + | A g
  1. Give the anode and cathode half-reactions.
  2. Write the overall equation for the chemical reaction.
  3. Give the direction of the current in the external circuit.
  1. In the standard notation format, the oxidation reaction is written on the left and the reduction reaction on the right. So, in this cell, zinc is oxidised and silver ions are reduced.

  2. Oxidation half-reaction:

    Z n Z n 2 + + 2 e -

    Reduction half-reaction:

    A g + + e - A g

  3. When you combine the two half-reactions, all the reactants must go on the left side of the equation and the products must go on the right side of the equation. The overall equation therefore becomes:

    Zn + Ag + + e - Zn 2 + + 2 e - + Ag

    Note that this equation is not balanced. This will be discussed later in the chapter.

  4. A build up of electrons occurs where oxidation takes place. This is at the zinc electrode. Current will therefore flow from the zinc electrode to the silver electrode.

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Uses and applications of the galvanic cell

The principles of the galvanic cell are used to make electrical batteries . In science and technology, a battery is a device that stores chemical energy and makes it available in an electrical form. Batteries are made of electrochemical devices such as one or more galvanic cells, fuel cells or flow cells. Batteries have many uses including in torches, electrical appliances (long-life alkaline batteries), digital cameras (lithium batteries), hearing aids (silver-oxide batteries), digital watches (mercury batteries) and military applications (thermal batteries). Refer to chapter [link] for more information on batteries.

The galvanic cell can also be used for electroplating . Electroplating occurs when an electrically conductive object is coated with a layer of metal using electrical current. Sometimes, electroplating is used to give a metal particular properties such as corrosion protection or wear resistance. At other times, it can be for aesthetic reasons for example in the production of jewellery. This will be discussed in more detail later in this chapter.

Galvanic cells

  1. The following half-reactions take place in an electrochemical cell: Fe Fe 3 + + 3 e - Fe 2 + + 2 e - Fe
    1. Which is the oxidation half-reaction?
    2. Which is the reduction half-reaction?
    3. Name one oxidising agent.
    4. Name one reducing agent.
    5. Use standard notation to represent this electrochemical cell.
  2. For the following cell:
    M g | M g 2 + | | M n 2 + | M n
    1. Give the cathode half-reaction.
    2. Give the anode half-reaction.
    3. Give the overall equation for the electrochemical cell.
    4. What metals could be used for the electrodes in this electrochemical cell?
    5. Suggest two electrolytes for this electrochemical cell.
    6. In which direction will the current flow?
    7. Draw a simple sketch of the complete cell.
  3. For the following cell:
    S n | S n 2 + | | A g + | A g
    1. Give the cathode half-reaction.
    2. Give the anode half-reaction.
    3. Give the overall equation for the electrochemical cell.
    4. Draw a simple sketch of the complete cell.

Questions & Answers

Is the normal force always 0
Mpilo Reply
define the term rate of reaction in word
David Reply
I think it a chemical process in which substance act mutually on each other.
Sphesihle
how many bones are in the human body?
Asali
what is wave lengh
mama Reply
is the de broglie wavelength of the particle
Hope
calcium and magnesium, which one can displace aluminum from its compound?
Markia Reply
how is aluminum ion formed?
Dickens
molecules with the same molecular formula but different chain
Malaza Reply
what will be the answer
.angel
chain isomer
Anele
what does the newton's law says?
there are 3 newtons laws which are newton's law of universal gravitation, law of cooling, law of motion
Imagine
Did the feather or leaf hit the ground first?
Shaloom Reply
leaf
Pradip
2 to 30 minut long distance race 20 km what's the avarage speed for the race
Jamilla Reply
what is meaning of covalent bonds
Lungani Reply
bonds that exists between non metal atoms. each atom contribute electron(s) which will form a bond joining the two atoms. electrons in the bond now belongs to both atoms
Matome
how do we name haloalkanes
Thobeka Reply
how do we name haloalkanes
lesedi
what are examples of haloalkanes
Mpho
haloalkanes are compounds that consist of the halogen group chlorine bromine flourine and so on like 2-bromobutan
Samkele
give an example of calculating work
Nwabisa Reply
what is chain Isomer?
Christian Reply
chain isomer ar compounds with the same molecular formular but different chain length
Samkele
Where does the functional group of ketone in carbons belong
Keletso Reply
alkane
Isamkele
how can I find the structural formulae and IUPAC names of hexane?
Matshidiso Reply
@Matshidiso identify your compound which is an alkane..the general formula for alkane is CnH2n+2... hex-6 substitute n with 6 implying that you'll have 6 carbons and 14 Hydrogens then you can draw your structural formula *NB* every carbon has to have 4 bonds
Kgabo
what are disadvantages of primary cells and advantage of secondary cells?
Thabang Reply

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Source:  OpenStax, Siyavula textbooks: grade 12 physical science. OpenStax CNX. Aug 03, 2011 Download for free at http://cnx.org/content/col11244/1.2
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